Relative effects of glycogen depletion and previous exercise on muscle force and endurance capacity.

Endurance capacity of human vastus lateralis muscles was observed 24 h after hard exercise followed by either a carbohydrate-restricted or a carbohydrate-loaded diet (depletion and repletion conditions). In a control condition the subjects did no previous exercise and ate their normal diet. Each of these conditions was followed by an experimental protocol in which the five male subjects made a series of alternating 25-s static contractions of each leg at 50% maximal voluntary contraction until one leg failed to achieve the required force (Tlim). Glycogen concentration before the experimental protocol in both legs was significantly lower in the depletion than in the repletion condition. Muscle lactate and creatine phosphate concentrations were within normal limits before the static contractions. The number of contractions the repleted (12.7 +/- 2.2) and depleted (10.3 +/- 1.5) legs could sustain before Tlim were not different from each other, but both were 35% (P less than 0.05) fewer than the control (17.6 +/- 3.0). Surface electromyogram (EMG) amplitude was higher in depleted than in repleted or control muscles. At Tlim, EMG amplitude was maximal, creatine phosphate was 50-70% depleted, and lactate increased fourfold. Average glycogen utilization per contraction in both the repletion and depletion conditions was 5.8 mmol/kg dry wt, but postexercise lactate concentrations were lower in depleted (14.4 +/- 3.6 mmol/kg dry wt) than in repleted (43.2 +/- 7.4) muscles. The EMG frequency distribution shifted downward in all conditions during the experimental protocol and was independent of muscle lactate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple factors limit exercise capacity in cystic fibrosis.

Exercise testing was performed in 50 patients with cystic fibrosis to determine whether hemodynamic factors limit exercise capacity in the disease. Prior to exercise testing, lung function and blood gas values were measured. Nutritional status was determined by calculating a weight for height (Wt for Ht) ratio for each subject. A progressive exercise test was used to determine maximum work capacity (Wmax). Cardiac output (Q) (indirect Fick method), and stroke volume (SV) were computed during steady-state exercise at 50% Wmax in 21 of 50 patients. Wmax, SV, Q, and lung function results are expressed as per cent predicted. The mean (+/- SD) Wmax was 75 +/- 23%. Multiple regression analysis showed that maximum voluntary ventilation, resting PaO2, and Wt for Ht accounted for 84% of the variance in Wmax. Although some patients had a reduced SV (mean = 96%) during steady-state exercise, all patients achieved a normal cardiac output (mean = 115%). SV correlated with resting PaO2 but not with lung function. We conclude that exercise capacity in cystic fibrosis is influenced by lung function, nutritional status, and resting hypoxemia, but not by cardiac function; the SV limitation noted in some patients may be due to increased pulmonary vascular resistance related to hypoxemia.